The Formosan subterranean termite, Coptotermes formosanus Shiraki, is a major worldwide pest that attacks both living trees and structural wood. Unlike other subterranean termites, the Formosan termite can establish a colony that does not touch the ground.
Coptotermes formosanus is native to southeast Asia, but is now also found in Hawaii, along the southeastern Atlantic coast of the United States, and in the Gulf South of the United States. First discovered in the United States by pest control operators in 1965, C. formosanus has gradually expanded its geographic domain. The largest single locus of C. formosanus in the United States is in south Louisiana, with heavy infestations in Lake Charles and New Orleans. C. formosanus may in some case displace native Reticultermes spp.
Three principal methods have been used in the past to control Coptotermes: (1) chemical and physical barriers to prevent termites from attacking wood, (2) wood preservatives and termiticides used to protect infested or susceptible wood, and (3) destruction of a termite colony by excavation of the nest. See, for example, U.S. Pat. Nos. 4,921,696; 5,303,523; 5,609,879; 5,802,779; and 5,874,097. The extensive use of chemical barriers and termiticides have generated public concern over environmental safety.
The search for a new repellent or termiticide is difficult because studies have shown that termites show unexpected sensitivity to chemicals, sensitivity that differs from that of other insects. For example, phenoxyethanol has been shown to be a trail-following substance; and naphthalene, a toxicant for most insects, was found to be used as fumigant by termites for their nests at concentrations that would kill fire ants. See U.S. Pat. No. 5,874,097; J. Chen et al., “Isolation and identification of 2-phenoxyethanol from a ballpoint pen as a trail-following substance of Coptotermes formosanus Shiraki and Reticulitermes sp., J. Entomol. Sci., vol. 33, pp. 97-105 (1998); and J. Chen et al., “Termites fumigate their nests with naphthalene,” Nature, vol. 392, pp. 558 (1998).
Natural termite repellent chemicals have also been described. The nature leaves of Cinnamomum osmophloeum Kaneh, and C. zeylanicum B1 have been found to impart termite resistance. The main components of oil extracted from these two species were cinnamic aldehyde and eugenol, respectively, with eugenol exhibiting the greater termite resistance activity. See Tien-shu Lin et al., “The effect of Cinnamomum spp. oils on the control of the termite Coptotermes formosanus Shiraki,” Taiwan For. Res. Inst. New Series, vol. 10, pp. 459-464 (1995). Additionally, the woods of Alaska-cedar, redwood, and teak were found to be resistant to Formosan subterranean termites. Although the termites did feed on the woods, it was only to a very limited extent. See J. K. Grace, “Natural resistance of Alaska-cedar, redwood, and teak to Formosan subterranean termites,” Forest Products Journal, vol. 44, pp. 41-45 (1994); and R. P. Adams, “Cedar Wood Oil—Analyses and Properties,” in Modern Methods of Plant Analysis—Oils and Waxes, H. F. Linskens and J. F. Jackon, eds., Spring Verlag, pp. 159-173 (1991).
Vetiver grass (Vetiveria zizanioides), a fast growing native of India, belongs to the same grass family group that includes maize, sorghum, sugarcane, and lemongrass. Vetiver is used to prevent soil erosion because the roots grow extremely fast. See Vetiver Grass: A Thin Green Line Against Erosion, Board on Science and Technology for International Development, National Research Council, National Academy Press, Washington, D.C. 177pp. (1993). In India, vetiver roots are woven into mats, baskets, fans, sachets, and ornaments. The woven mats are believed to provide protection from insect pests, in addition to their pleasant fragrance. Although the dried roots have been used to repel clothes moths, head lice, and bedbugs, termites are reported to eat vetiver grass. Sugarcane, a member of the same grass family, is even known to be a preferred food of the Formosan subterranean termite. See Vetiver Grass: A Thin Green Line Against Erosion, p. 63 and 81 (1993); and J. Chen et al., “Determination of feeding preference of Formosan subterranean termite (Coptotermes formosanus Shiraki) for some amino acid additives,” J. Chem. Ecol., vol. 23, pp. 2359-2369 (1996). Despite this knowledge of termite feeding, solid bands of vetiver grass have been speculated to potentially block termites, fire ants, or other insidious underground insects because other insects were known to avoid vetiver oil and vetiver roots. See Vetiver Grass: A Thin Green Line Against Erosion, pp. 24, 28, 80 and 92 (1993).
Vetiver oil extracted from the roots is used in the soap and perfume industry because of its pleasant and persistent fragrance. See U.S. Pat. No. 4,937,073. Vetiver oil is known to be a complex mixture of over 300 compounds, over 150 of which are sesquiterpenoid compounds. See P. Weyerstahl et al., “New sesquiterpene ethers from vetiver oil,” Liebigs Ann., pp. 1195-1199 (1996); N. H. Andersen, “The structures of zizanol and vetiselinenol,” Tetrahedron Letters, vol. 21, pp. 1755-58 (1970); R. M. Coates et al., “The crystal structure of khusimol p-bromobenzoate,” Chemical Communications, pp. 999-1000 (1969). Vetiver oil is known to repel flies and cockroaches. The ingredient in vetiver oil reported to repel insects are the ketones- α-vetivone, β-vetivone, khusimone; and the aldehydes—zizanal, and epizizanal. See Vetiver Grass: A Thin Green Line Against Erosion, p. 80 and 92 (1993); and Jain et al., “Insect Repellents from Vetiver Oil: I. Zizanal and Epizizanal,” Tetrahedron Letters, vol. 23, pp. 4639-4642 (1982). Other components of vetiver oil are zizanol (or khusimol), bicyclovetivenol and α-cedrene. See N. Andersen, “Biogenetic implications of the antipodal sesquiterpenes of vetiver oil,” Phytochemistry, vol. 9, pp. 145-151 (1970); R. M. Coates et al., “The crystal structure of khusimol p-bromobenzoate,” Chemical Communications, Com. 1099, pp. 990-1000 (1969); and R. Kaiser et al., “Biogenetically significant components in vetiver oil,” Tetrahedron Letters, vol. 20, pp. 2009-2012 (1972).
Nootkatone, or 4,4a5,6,7,8-hexahydro-6-isopropenyl-4,4a-dimethyl-2(3H)-naphthalenone, is a mildly pungent sesquiterpene ketone found in the oil of Alaska yellow cedar (Chamaecyparis nootkatensis) and in a great number of citrus oil, especially oil from grapefruit (Citrus pavadisi). Nootkatone is widely used in the perfumery and flavor industries being essentially non-toxic to humans. See U.S. Pat. Nos. 3,835,192 and 5,847,226; H. Erdtman et al., “The Chemistry of the Natural Order Cupressales XVIII: Nootkatone, a new sesquiterpene type hydrocarbon from the heartwood of Chamaecyparis nootkatensis (Lamb.) Spach.,” Acta Chem. Scand., vol. 11, pp. 1557 (1957); and H. Erdman et al., “The Chemistry of the Natural Order Cupressales 46. The structure of nootkatone,” Acta Chem. Scand., vol. 16, pp. 1311 (1962). Nootkatone has also been identified as a minor component of vetiver oil. See U.S. Pat. No. 4,937,073; and N. H. Andersen et al., “Prezizaene and the biogenesis of zizaene,” Chemistry and Industry, pp. 62-63 (1971); N. Andersen, “Biogenetic implications of the antipodal sesquiterpenes of vetiver oil,” Phytochemistry, vol. 9, pp. 145-151 (1970); and R. Kaiser et al., “Biogenetically significant components in vetiver oil,” Tetrahedron Letters, vol. 20, pp. 2009-2012 (1972). The structure of nootkatone is shown below: 